Nitride semiconductor light emitting device and fabricating method thereof

ABSTRACT

A nitride semiconductor light emitting device including: a first nitride semiconductor layer; an active layer formed on the first nitride semiconductor layer and including at least one barrier layer grown under hydrogen atmosphere of a high temperature; and a second nitride semi conductor layer formed on the active layer, and a method of fabricating the same are provided. According to the light emitting device and method of fabricating the same, the light power of the light emitting device is increased and the operation reliability is enhanced.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of application Ser. No. 10/592,573filed on Sep. 12, 2006 now U.S. Pat. No. 7,728,338, which claimspriority to Application No. 10-2004-0092097 filed in the Republic ofKorea on Nov. 11, 2004. The entire contents of all of the aboveapplications is hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a nitride semiconductor light emittingdevice and fabrication method thereof, and more particularly, to anitride semiconductor light emitting device and fabrication methodthereof that can enhance the light power and reliability of the lightemitting device.

BACKGROUND ART

In general, nitride semiconductors are in the limelight as a materialfor blue light emitting diodes, blue laser diodes or the like.

FIG. 1 is a sectional view of a general nitride semiconductor lightemitting device.

Referring to FIG. 1, the general nitride semiconductor light emittingdevice includes a sapphire substrate 110, a buffer layer 120 formed onthe sapphire substrate 110, an n-type nitride semiconductor layer 130formed on the buffer layer 120, an active layer 140 formed on the n-typenitride semiconductor layer 130, and a p-type nitride semiconductorlayer 150 formed on the active layer 140.

The n- and p-type nitride semiconductor layers 130 and 150 are formed bydoping a variety of dopants into a gallium nitride (GaN). Representativeexample of n-type dopants includes silicon (Si), and representativeexample of p-type dopants includes magnesium (Mg).

The active layer is a layer through which light emits. As arepresentative growth method of the active layer, and is generally madein an InXGa1−XN(0≦x≦1) single well structure or multi-well structure inwhich Indium (In) and gallium (Ga) are contained in predeterminedratios. The active layer of InXGa1−XN(0≦x≦1) is generally grown under anenvironment of nitrogen atmosphere and at a temperature of less than900° C.

In detail, a general growth method below 900° C. is performed in anitrogen (N2) atmosphere for a proper composition ratio of In and Ga.However, in the thin film growth of InXGa1−XN(0≦x≦1), as the Inintroduction amount into GaN increases or the Ga introduction amountinto InN increases, a serious phase dissociation phenomenon occurs,which is problematic. To solve such a phase dissociation phenomenon, ifthe growth temperature is increased, In phase dissociation phenomenonincreases, which makes it difficult to obtain a good quality thin layer.

Meanwhile, when the active layer is grown in a relatively lowtemperature, In segregation occurs from thin InGaN layer, whichdeteriorates the layer quality, and many crystal defects also occur atan interface between InXGa1−XN(0≦x≦1) and GaN due to a latticedifference therebetween. Also, the In phase dissociation phenomenonincreases, which makes it difficult to obtain a good quality layer, andalso the occurring crystal defects are combined with crystal defects ofa lower structure to decrease the light emitting efficiency and thedevice reliability.

Finally, in the related art growth method, in the case of the materials,such as InGaN/GaN, a strong piezo electric field is generated inside theactive layer because of a stress due to a large lattice mismatch, andelectron-hole wave functions are separated, resulting in a deteriorationin the light emitting efficiency.

DISCLOSURE OF INVENTION Technical Problem

The present invention is to provide a nitride semiconductor lightemitting device that can enhance the crystallinity of InXGa1−XN(0≦x≦1)constituting an active layer by decreasing crystal defects due to alarge lattice mismatch between InXGa1−XN(0≦x≦1) and InYGa1−YN(0≦y≦1) ofa nitride semiconductor.

Also, the present invention is to provide a nitride semiconductor lightemitting device having a low driving voltage and a high light emittingefficiency in which the light emitting efficiency is increased due to athin active layer having InXGa1−XN(0≦x≦1) of In composition and afabrication method thereof.

Also, the present invention is to provide a nitride semiconductor lightemitting device having an enhanced light power and reliability and afabrication method thereof.

Technical Solution

There is provided a nitride semiconductor light emitting deviceincluding: a first nitride semiconductor layer; an active layer formedon the first nitride semiconductor layer and including at least onebarrier layer grown under hydrogen atmosphere of a high temperature; anda second nitride semiconductor layer formed on the active layer.

Also, there is provided a nitride semiconductor light emitting deviceincluding: a buffer layer; a first nitride semiconductor layer formed onthe buffer layer; an active layer formed on the first nitridesemiconductor layer and including at least a pair of a well layer and abarrier layer having an IN(indium) composition ratio of less than 10%;and a second nitride semiconductor layer formed on the active layer.

Also, there is provided a method of fabricating a nitride semiconductorlight emitting device, the method including: forming a first nitridesemiconductor layer; forming an active layer on the first nitridesemiconductor layer, the forming of the active layer including forming awell layer and a barrier layer grown under a hydrogen atmosphere at ahigh temperature; and forming a second nitride semiconductor layer onthe active layer.

Advantageous Effects

According to the nitride semiconductor light emitting device of thepresent invention, a barrier layer grown in a hydrogen atmosphere at ahigh temperature decreases crystal defects due to a large latticemismatch between a well layer and the barrier layer constituting theactive layer and enhances the crystallinity of the active layer.

Also, the light emitting device with a high light power and an increasedreliability can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

The spirit of the present invention will be understood from theaccompanying drawings. In the drawings:

FIG. 1 is a sectional view of a general nitride semiconductor lightemitting device;

FIG. 2 a sectional view of a nitride semiconductor light emitting deviceaccording to a first embodiment of the present invention;

FIG. 3 a sectional view of a nitride semiconductor light emitting deviceaccording to a second embodiment of the present invention; and

FIG. 4 a sectional view of a nitride semiconductor light emitting deviceaccording to a third embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to accompanying drawings.

First Embodiment

FIG. 2 a sectional view of a nitride semiconductor light emitting deviceaccording to a first embodiment of the present invention.

Referring to FIG. 2, the nitride semiconductor light emitting deviceaccording to the present invention includes a buffer layer 220 formed ona substrate 210, an n-type nitride semiconductor layer 230 formed on thebuffer layer 220, an active layer 240 formed on the n-type nitridesemiconductor layer 230, the active layer 240 including well layers 241a, 249 a and barrier layers 241 b, 249 b, and a p-type nitridesemiconductor layer 250 formed on the active layer 240.

In detail, the active layer 240 is formed between the n-type nitridesemiconductor layer 230 and the p-type nitride semiconductor layer 250.In particular, the active layer 240 is characterized by including thebarrier layers 241 b, 249 b grown in a high temperature hydrogenatmosphere so as to reduce crystal defects.

Also, the active layer 240 may have a single quantum well structureconsisting of a first well layer 241 a and a first barrier layer 241 b,or a multi-quantum well structure consisting of a plurality of welllayers 241 a, 249 a and a plurality of barrier layers 241 b, 249 balternatively formed. Preferably, the plurality of well layers 241 a,249 a and the plurality of barrier layers 241 b, 249 b are arranged toinclude 4 to 10 pairs of periodically repeated well layers and barrierlayer, each pair consisting of one well layer and one barrier layer.

Also, it is preferable that each of the well layers 241 a, 249 a shouldhave a composition of InXGa1−XN(0≦x≦1) of which In composition ratio is10-20% and each of the barrier layers 241 b, 249 b should have acomposition of InYGa1−YN(0≦y≦1) of which In composition ratio is below10%.

Hereinafter, a method of fabricating a nitride semiconductor lightemitting device according to an embodiment of the present invention willbe described.

First, a buffer layer 220 is formed on a substrate 210. The substrate210 may be a sapphire substrate, a silicon substrate or a siliconcarbide (SiC) substrate, which are widely used in the nitridesemiconductor light emitting devices.

Next, an n-type nitride semiconductor layer 230 serving as a firstnitride semiconductor layer is formed on the buffer layer 220. After then-type nitride semiconductor layer 230 is formed, a process step offorming an active layer 240 is performed.

Describing the process step of forming the active layer 240 in moredetail, a well layer 241 a having a composition of InXGa1−XN(0≦x≦1) isformed on the n-type nitride semiconductor layer 230. Preferably, thewell layer 241 a is formed with a composition of InXGa1−XN(0≦x≦1) ofwhich In composition ratio is 10% to 20%. After the well layer 241 a isformed, a barrier layer 241 b having a composition of InYGa1−YN(0≦y≦1)is formed on the well layer 241 a. Preferably, the barrier layer 241 bis formed with a composition of InYGa1−YN(0≦y≦1) of which In compositionratio is below 10%.

Herein, the barrier layer 241 b is formed at a thickness range of 30-200Å in a high temperature hydrogen atmosphere. If the barrier layer 241 bis formed so thin, the crystal defects-removing effects, such asdefects, inclusion or the like generated in a boundary betweenInXGa1−XN(0≦x≦1) and InYGa1−YN(0≦y≦1) constituting the well layers andthe barrier layers, are decreased, so that the device performanceenhancement effect is reduced. Accordingly, it is preferable that thebarrier layer 241 b be 30 Å or more thick. Further, if the barrier layer241 b is formed so thick, the resistance, which is happening duringfabrication of device, is increased, so that the electricalcharacteristics and the light emitting efficiency of the device arelowered. Accordingly, it is preferable that the barrier layer 241 b be200 Å or less thick. Resultantly, it is preferable that the barrierlayer 241 b be formed at a thickness range of 30-200 Å.

In addition, when the barrier layer 241 b is formed in the hydrogenatmosphere above 900° C. according to the present invention, it showsremarkably decreased crystal defects, compared with the related artbarrier layer of InYGa1−YN(0≦y≦1) having a multi-well structure formedin a temperature below 900° C. However, if the growth temperature of thebarrier layer 241 b exceeds 1,040° C., the crystal defects increase. Tothis end, it is preferable that the temperature range for the formationof the barrier layer 241 b be in a range of 900-1,040° C.

By the above process steps, the active layer 240 is formed with a singlequantum well structure consisting of a single well layer 241 a and asingle barrier layer 241 b or a multi-quantum well structure consistingof a plurality of well layers and barrier layers alternatively arranged.

After the active layer 240 is formed, a p-type nitride semiconductorlayer 250 serving as a second nitride semiconductor layer is formed onthe active layer 240.

The barrier layer suppresses crystal defects existing in the lowerstructure of the substrate 210, the buffer layer 220 and the n-typenitride semiconductor layer 230 and dislocations such as defects orinclusions occurring in a boundary between InXGa1−XN(0≦x≦1) andInYGa1−YN(0≦y≦1) from being propagated, thereby enhancing the devicereliability. Hence, the light power of the light emitting device isimproved and the device reliability is increased.

Second Embodiment

Hereinafter, a nitride semiconductor light emitting device andfabrication method thereof according to a second embodiment of thepresent invention will be described.

FIG. 3 a sectional view of a nitride semiconductor light emitting deviceaccording to a second embodiment of the present invention.

Referring to FIG. 3, the nitride semiconductor light emitting deviceaccording to the present invention includes a buffer layer 320 formed ona substrate 310, an n-type nitride semiconductor layer 330 formed on thebuffer layer 320, an active layer 340 formed on the n-type nitridesemiconductor layer 330, the active layer 340 including at least barrierlayers 341 b, 349 b, and a p-type nitride semiconductor layer 350 formedon the active layer 340.

The active layer 340 is formed between the n-type nitride semiconductorlayer 330 and the p-type nitride semiconductor layer 350. The activelayer 340 includes the barrier layers 341 b, 349 b grown in a hightemperature nitrogen atmosphere so as to decrease crystal defects. Oneperiod of the active layer 340 includes a first well layer 341 a formedon the n-type nitride semiconductor layer 330, a first barrier layer 341b grown on the first well layer 341 a in a high temperature hydrogenatmosphere, and a seed layer 341 c formed on the first barrier layer 341b.

In detail, the active layer 340 includes a plurality of well layers 341a, 349 a, a plurality of barrier layers 341 b, 349 b and a plurality ofseed layers 341 c, 349 c alternatively arranged. Preferably, theplurality of well layers 341 a, 349 a, the plurality of barrier layers341 b, 349 b and the plurality of seed layers 341 c, 349 c, one periodconsisting of one well layer, one barrier layer and one seed layer, areformed in four or ten periods.

The seed layers 341 c, 348 c are grown with a composition ofInZGa1−ZN(0<z<1) or a single layer of InN. The seed layers serve as aseed while the well layers are formed directly on the seed layers suchthat In is sufficiently introduced into the well layers.

The nitride semiconductor light emitting device thus formed according tothe second embodiment of the present invention is characterized byincluding forming the seed layers prior to forming the well layers suchthat the characteristics of the well layers are improved and In issufficiently supplied into the well layers.

Hereinafter, a method of fabricating the nitride semiconductor lightemitting device according to the second embodiment of the presentinvention will be described in detail.

First, a buffer layer 320 is formed on a substrate 310. Next, an n-typenitride semiconductor layer 330 serving as a first nitride semiconductorlayer is formed on the buffer layer 320. After the n-type nitridesemiconductor layer 330 is formed, a process step of forming an activelayer 340 is performed.

To form the active layer 340, a well layer 341 a having a composition ofInXGa1−XN(0≦x≦1) is formed on the n-type nitride semiconductor layer330. After the well layer 341 a is formed, a barrier layer 341 b isformed on the well layer 341 a. Since the process steps from the formingof the n-type nitride semiconductor layer 330 to the forming of thebarrier layer 341 b are the same as those in the first embodiment, theirdetailed description will be omitted.

After the barrier layer 341 b is formed, a seed layer 341 c is formedwith a composition of InZGa1−ZN(0<z<1) or in a single layer of InN. Theseed layer 341 c serves as a seed while a well layer 342 a is formedwith a composition of InXGa1−XN(0≦x≦1) such that In is sufficientlysupplied into the well layer 342 a with a composition ofInXGa1−XN(0≦x≦1). Accordingly, a carrier localization caused by a phasedissociation of the inside of the well layer or a non-uniform Incomposition becomes adjustable. Meanwhile, a composition ratio of In inthe seed layer 341 c with a composition of InZGa1−ZN is preferably above10% to an overall composition.

In a general case, the well layer with a composition of InXGa1−XN(0≦x≦1)has a composition ratio containing 15% In. In order to increase the Incomposition ratio of the well layer 342 a in the nitride semiconductorlight emitting device according to the present invention, the Incomposition ratio in InZGa1−ZN(0<z<1) constituting the seed layer 341 cis made above 10%. By doing so, In introduction effect into the welllayer increases, so that the well layer 342 a can be formed with acomposition ratio containing 15% or more In.

The seed layer 341 c of a single layer of InZGa1−ZN(0<z<1) or InN ispreferably grown at a thickness below 20 Å. This is because if the seedlayer 341 c is thicker than the well layer 342 a, In isolationphenomenon may occurs at a boundary between the seed layer 341 c and thewell layer 342 a, which results in the deterioration in the layerquality or in the light emitting characteristic.

After the seed layer 341 c is grown, a heat treatment of the seed layer341 c may be added. Example of the heat treatment includes a processstep of thermally annealing the seed layer 341 c at the same temperatureas the growth temperature of the seed layer 341 c or a process step ofelevating the growth temperature while the well layer 342 b is grown.The above heat treatment promotes In introduced into the seed layer 341c to form a lattice bond with Nitrogen(N) and also helps Ga and In tobond with each other while the well layer 342 a is formed.

After the seed layer 341 c is formed, well layer 342 a is formed with acomposition of InXGa1−XN(0≦x≦1). While the well layer 342 a is formedwith the composition of InXGa1−XN(0≦x≦1), a sufficient amount of In isintroduced into the well layer 342 a from the seed layer 341 c formed inthe previous process step. Accordingly, a high temperature growth ofactive layer can be induced to obtain thin active layer having the highquality composition of InXGa1−XN(0≦x≦1).

Resultantly, a nitride semiconductor light emitting device having a highlight emitting efficiency can be obtained due to the carrierlocalization effect of the high quality thin InGaN layer having the highIn composition ratio.

Through the above process steps, a single quantum well structureconsisting of the well layer 341 a/barrier layer 341 b/seed layer 341 ccan be obtained or a multi-quantum well structure further including aplurality of well layers/barrier layers/seed layers additively grown onthe seed layer 341 c of the single quantum well structure can beobtained.

In forming the final quantum well structure of the active layer 349, thewell layer 349 a and the barrier layer 349 b are formed, but the seedlayer is omitted, which is because an additional well layer does notexist on the seed layer if formed, and the barrier layer 349 b directlycontacts the p-type nitride semiconductor layer 350 to obtain a normaloperation environment of light emitting device due to the formation of acontact layer.

Subsequently, a p-type nitride semiconductor layer serving as a secondnitride semiconductor layer 350 is formed on the active layer 340.

Elements, which are not particularly described in the above descriptionfor the second embodiment, can be referred from the description of thefirst embodiment.

The characteristics of the nitride semiconductor light emitting deviceaccording to the second embodiment will now be described.

The barrier layers 341 b, 349 b in the active layer 340 are grown in thehigh temperature hydrogen atmosphere to reduce the crystal defects.Accordingly, the crystal defects of the lower structure including thesubstrate 310, the buffer layer 320 and the n-type nitride semiconductorlayer 330, and the dislocations, such as the defects or inclusions,occurring at the boundary between InXGa1−XN(0≦x≦1) and InYGa1−YN(0≦y≦1),can be prevented from being propagated, thereby enhancing the devicereliability.

Also, while the nitride semiconductor light emitting device according tothe present invention is fabricated, the seed layers 341 c, 348 c helpIn to be sufficiently introduced into the well layers 342 a, 349 ahaving the composition of InXGa1−XN(0≦x≦1) during the growth of the welllayers 342 a, 349 a. The above behavior of the seed layers 341 c, 348 cinduces a natural rise of the growth temperature being caused by thehigh In composition ratio such that a thin InGaN layer grown at a hightemperature can be obtained, thereby enhancing the light emittingefficiency due to the carrier localization effect.

Recent research results show that an energy band gap of InN is a verysmall value of 0.7 eV (corresponds to a wavelength of 1,771 nanometers),which means that the energy gap of InXGa1−XN(0≦x≦1) includes infraredray region to ultra violet ray region. Accordingly, it is possible tofabricate an LCD emitting lights at all wavelengths.

However, according to the nitride semiconductor light emitting deviceand fabrication method thereof provided in the first and secondembodiments, since the first well layers 241 a, 341 a are grown directlyon the n-type nitride semiconductor layers 230, 330, respectively, thelattice structure defects of the first well layers 241 a, 341 a may notbe sufficiently reduced.

Third Embodiment

The third embodiment of the present invention is provided to solve theabove drawback, and provides a fabrication method with a structure thatcan cope with the lattice structure defects of the first well layers 241a, 341 a first grown.

FIG. 4 a sectional view of a nitride semiconductor light emitting deviceaccording to a third embodiment of the present invention.

Referring to FIG. 4, to solve lattice structure defects of a first welllayer 441 a, an additional barrier layer 439 is further formed betweenthe first well layer 441 a and an n-type nitride semiconductor layer430, which is to remove the crystal defects of the first well layer 441a and at the same time to stably operate the light emitting device. Theadditional barrier layer 439 is grown in a high temperature hydrogenatmosphere.

The process step of forming the additional barrier layer 439 isperformed between the process step of forming the aforementioned n-typenitride semiconductor layer 430 and the process step of forming thefirst well layer 441 a.

Through the method of fabricating the nitride semiconductor lightemitting device according to the third embodiment of the presentinvention, the crystal defects existing of the lower structure includinga substrate 410, a buffer layer 420 and the n-type nitride semiconductorlayer 430 can be prevented from being propagated to the first well layer441 a. Also, dislocations such as defects or inclusions occurring at aboundary between the well layer having the composition ofInXGa1−XN(0≦x≦1) and the barrier layer having the composition ofInYGa1−YN(0≦y≦1) can be efficiently prevented from being propagated,thereby minimizing the crystal defects of the active layer.

Industrial Applicability

According to the nitride semiconductor light emitting device of thepresent invention, the barrier layer grown in a high temperaturehydrogen atmosphere decreases crystal defects due to a large latticemismatch between the well layer having the composition ofInXGa1−XN(0≦x≦1) and the barrier layer having the composition ofInYGa1−YN(0≦y≦1) and enhances the crystallinity of the active layerhaving the composition of InXGa1−XN(0≦x≦1).

Also, the seed layer having the composition of InZGa1−ZN(0≦z≦1) of whichIn content is high can increase the light emitting efficiency and allowlight having a wide wavelength band to be obtained.

In addition, a nitride semiconductor light emitting device with animproved light power and reliability can be obtained.

1. A semiconductor light emitting device, comprising: a first conductivetype semiconductor layer; an active layer formed on the first conductivetype semiconductor layer, wherein the active layer is a multi-quantumwell structure having a plurality of well layers alternatively stackedwith a plurality of barrier layers; and a second conductive typesemiconductor layer formed on the active layer, wherein a first welllayer of the plurality of well layers has a composition ofIn_(X)Ga_(1-X)N (0≦x≦1) with an In (Indium) composition ratio of 10-20%,wherein a first barrier layer of the plurality of the barrier layers isformed on the first well layer and has a composition of In_(Y)Ga_(1-Y)N(0≦Y≦1) with an In (Indium) composition ratio of less than 10%, whereinthe active layer comprises 4 to 10 pairs of periodically repeated welllayers and barrier layers, each pair including a corresponding barrierlayer on a corresponding well layer, wherein one of the pairs ofperiodically repeated well layers and barrier layers comprises a seedlayer of InN, and wherein an upper surface of the seed layer is indirect contact with a lower surface of the corresponding well layer anda lower surface of the seed layer is in direct contact with an uppersurface of the corresponding barrier layer.
 2. The semiconductor lightemitting device of claim 1, wherein the first barrier layer has athickness of 30-200 Å.
 3. The nitride semiconductor light emittingdevice of claim 1, wherein the first well layer is interposed betweenthe first barrier layer and the first conductive type semiconductorlayer.
 4. The semiconductor light emitting device of claim 1, wherein asecond barrier layer of the plurality of the barrier layers isinterposed between the first conductive type semiconductor layer and thefirst well layer.
 5. The semiconductor light emitting device of claim 1,wherein a thickness of the seed layer is less than a thickness of thebarrier layer.
 6. A semiconductor light emitting device, comprising: afirst conductive type semiconductor layer; an active layer formed on thefirst conductive type semiconductor layer; and a second conductive typesemiconductor layer formed on the active layer, wherein the active layercomprises at least two pairs of periodically repeated well layers andbarrier layers, each pair including a corresponding barrier layer on acorresponding well layer, each well layer having a composition ofIn_(x)Ga_(1-x)N (0≦x≦1) wherein at least one of the barrier layers is30-200 Å thick, wherein one of the pairs of periodically repeated welllayers and barrier layers comprises a seed layer, wherein the seed layerhas a thickness smaller than a well layer thickness, and wherein anupper surface of the seed layer is in direct contact with a lowersurface of a corresponding well layer and a lower surface of the seedlayer is in direct contact with an upper surface of a correspondingbarrier layer.
 7. The semiconductor light emitting device of claim 6,wherein the well layers have a composition of In_(X)Ga_(1-X)N (0≦x≦1)with an In (Indium) composition ratio of 10-20%, and wherein the barrierlayers have a composition of In_(Y)Ga_(1-Y)N (0≦Y≦1) with an In (Indium)composition ratio of less than 10%.
 8. The semiconductor light emittingdevice of claim 7, wherein the first conductive type semiconductor layercomprises an n-type semiconductor layer, and wherein the secondconductive type semiconductor layer comprises a p-type semiconductorlayer.
 9. The semiconductor light emitting device of claim 6, whereinthe seed layer has an In (Indium) composition ratio of more than 10%.10. The semiconductor light emitting device of claim 6, wherein seedlayer has an energy gap of In_(x)Ga_(1-x)N(0≦x≦1) including an infraredray region to an ultra violet ray region.
 11. The semiconductor lightemitting device of claim 6, wherein the seed layer is a continuous layerhaving a thickness of 20 Å or less.
 12. The semiconductor light emittingdevice of claim 9, further comprising: a buffer layer formed under thefirst conductive type semiconductor layer; and a substrate formed underthe buffer layer.
 13. The semiconductor light emitting device of claim6, wherein the In (Indium) composition ratio of the seed layer is equalto or different from an In (Indium) composition ratio of thecorresponding well layer of the two pairs, and wherein the In (Indium)composition ratio of the corresponding well layer of the two pairs isgreater than the In (Indium) composition ratio of the correspondingbarrier layer of the two pairs.
 14. The semiconductor light emittingdevice of claim 6, wherein the seed layer is formed of InN.